Cataract surgery involves the removal of the lens or lens nucleus from the eye of a patient, and it is common in such procedures to implant within the eye an artificial intraocular lens, the lens being supported in either the anterior or posterior chambers and being supported by wires or other structure that extend from the lens outwardly into contact with supportive, circumferential grooves or other structure adjacent the iris.
Typical intraocular lenses are disclosed in the following references:
U.S. Pat. No. 4,092,743 (Kelman) PA0 U.S. Pat. No. 4,174,543 (Kelman) PA0 U.S. Pat. No. 4,261,065 (Tennant) PA0 U.S. Pat. No. 4,328,595 (Sheets) PA0 U.S. Pat. No. 4,338,687 (Rainin) PA0 U.S. Pat. No. 4,340,979 (Kelman) PA0 U.S. Pat. No. 4,343,050 (Kelman) PA0 U.S. Pat. No. 4,370,760 (Kelman)
Intraocular lenses in general are characterized by including a central lens or lenticular portion, and two or more struts, usually radially resilient, that extend outwardly of the lens and which gently but elastically engage appropriate circumferential eye structure adjacent the iris. The struts of intraocular lenses that are to be employed in the anterior chamber of the eye commonly engage the internal scleral sulcus, commonly called the "angle", formed between the iris and the internal periphery of the cornea, avoiding substantial contact or interference with the trabacular meshwork. Intraocular lenses intended to be mounted in the posterior chamber commonly have struts or other fixation devices that engage the ciliary recess or the circumferential edges of the posterior lens capsule that remains after removal of the lens nucleus.
In normal human eyes, aqueous humor is discharged into the posterior chamber, flows through the pupil into the anterior chamber, and is removed from the anterior chamber by means of the trabacular meshwork and Schlemm's canals adjacent the internal scleral recess. When the flow of aqueous humor in this manner is restricted or blocked, as may occur when the anterior face of the vitreous humor comes forward into contact with the iris following cataract surgery, acute glaucoma can result. Accordingly, one or more small surgical iridectomies are routinely performed in the iris during cataract surgery to provide alternate flow paths for aqueous humor. Peripheral iridectomies preferably are basal, that is, they are formed at the periphery of the iris. Non-basal peripheral iridectomies, formed in the iris at positions spaced inwardly from its periphery, have also been used but are less preferred in that they can become blocked or plugged by the anterior vitreous face.
Intraocular lenses commonly are surgically oriented so that their supporting structure is rotated out of alignment with basal peripheral iridectomies, and it generally is expected that the rotational position of intraocular lenses will remain fixed permanently. Intraocular lenses commonly are formed with small holes or indentations adjacent the lens periphery to accept instruments enabling surgeons to rotate the lenses into desired positions spaced rotationally from openings formed through basal peripheral iridectomy procedures.
Unfortunately, intraocular lenses seldom remain permanently fixed against rotation with respect to the lens axis. The lenses may in fact be rotationally displaced through commonplace rubbing of the eyes, with the result that the lens fixation elements over a period of months or years may come into contact with and may actually enter basal peripheral iridectomies formed during cataract surgery. Inflammation of the iris (iritis) may result, but more importantly, the lens itself, due to the resulting loss of placement of its fixation elements, may tilt or may become dislocated with respect to the pupillary axis. The lens itself, if implanted in the anterior chamber, may touch and cause severe damage to the inner corneal surface, or, if placed in the posterior chamber, may cause rupture of the anterior vitreous face causing vitreous prolapse into the iridectomy wound, in turn leading to cystoid macular (retinal) edema. The undesired rotation of intraocular lenses in this manner, and the resulting problems that arise, have only recently been recognized. Unfortunately, such problems often arise months or years after a lens has been implanted and routine consultation with a surgeon has been terminated. As a result, severe damage to the eye can readily occur before corrective surgical steps can be taken.
Certain of the fixation elements previously employed with intraocular lenses are of wire or of a springy, wire-like material. The wire is formed into a "U"-shaped loop with the ends of the loop each being fixed to the lens. To the extent that the loops are smoothly curved, protrusion into or through an iridectomy opening may be avoided; however, the fixation of such loops at both ends to the lens reduces the elasticity of the loops. The lens with the semi-rigid fixation loops accordingly is difficult to insert and properly place within the eye since the loops are not highly elastic and are deformed only with some difficulty. It has been proposed in U.S. Pat. 4,338,687 to provide the lens itself with internal springs which resiliently receive ends of the "U"-shaped loops to enable the loops as a whole to be elastically moved toward and away from the lens periphery. This lens structure, however, is quite complicated and expensive. The increase in lens thickness required to accommodate the spring mechanism adds substantial weight to the device, resulting in increased potential damage to eye structures.